Mirum, Incyte's zilurgisertib cuts FOP lesions 81% as FDA starts Priority Review

Key Takeaways:

Zilurgisertib cut new HO lesion formation by 81% vs placebo at Week 24.
FDA granted Priority Review with a decision deadline of Sept. 26, 2026.
Mirum shares rose 25.7% YTD; Incyte gained 9.9% in the same period.

Mirum Pharmaceuticals and Incyte said zilurgisertib reduced new bone lesion formation by 81% in a Phase II FOP trial, as the FDA began Priority Review of the new drug application.

"These data demonstrate zilurgisertib's potential to fundamentally alter the course of this devastating disease," the companies said in a joint statement announcing the PROGRESS study results.

The pivotal Phase II PROGRESS study enrolled 63 patients aged 12 years and older with fibrodysplasia ossificans progressiva, an ultra-rare genetic disorder in which soft tissues progressively transform into bone. Patients were randomized equally to receive either zilurgisertib 100 mg once daily or placebo for 24 weeks, followed by an open-label extension. At Week 24, only one patient (3.1%) in the treatment arm developed a new heterotopic ossification lesion compared with five patients (16.7%) in the placebo group — an 81% reduction. The mean volume of new lesions was nearly eliminated in the treatment arm, representing a 99.9% reduction versus placebo.

Secondary endpoints showed consistent benefit. Total HO lesion volume declined in treated patients while increasing in the placebo group. Annualized flare activity was lower in the zilurgisertib arm. Through 48 weeks in the open-label extension, no new HO lesions appeared in patients who continued treatment or crossed over from placebo. The safety profile was favorable, with most adverse events rated mild to moderate and no discontinuations or dose reductions reported.

FOP affects an estimated 800 to 1,000 patients in the US, with no approved therapies that modify disease progression. The FDA accepted the NDA under Priority Review, shortening the standard 10-month review to six months, with a decision deadline of Sept. 26, 2026. Mirum licensed worldwide development and commercialization rights from Incyte.

The positive data and regulatory milestone represent a significant derisking event for both companies. Mirum shares have gained 25.7% year to date, and Incyte shares have risen 9.9%, compared with a 1.4% decline in the broader industry. Investors will watch for the FDA's decision in September, which could make zilurgisertib the first approved treatment for FOP.

This article is for informational purposes only and does not constitute investment advice.